There are many instances where it is necessary to separate a gas from a liquid that may also contain particles, while maintaining pressure in a separator. One such example is the case of a well that is producing gases, liquids and particles. This is typical of wells that are producing gas from coal seams. Here there are frequently two streams coming from the well. One is from the well pump, which is producing water containing gas and coal fines. The other comes from the annulus and is mostly comprised of gas mixed with some water and occasionally some particles.
Most wells now have fitted to them separators that are essentially pressure vessels with a gas outlet at the top, and a valve to let out liquids in the bottom that is opened by various means. The separation is essentially brought about by stilling the liquid in the separator and letting gravity do the separation. One of the disadvantages of such a separator is that solids may consolidate in the bottom and block the release of the liquid. In addition the efficiency of the separator is limited by gravitational forces.
Cyclonic separators have been in use for a long time. They operate by having the inlet fluid enter a tubular separator tangentially. The swirling motion induces a radial acceleration which acts on the fluid causing more dense materials to be forced near the wall of the cyclone where they slow and are pulled down by gravitational force to the cyclone base where they are discharged. Such cyclones are typically used in the separation of particulate ores from liquids. In this application they are generally referred to as hydrocyclones. The discharge from the top in these cases is a less dense media, along with a dense media from the bottom of the hydrocyclones. Cyclonic devices are also used to clean particulate matter from air such as in internal combustion engine air cleaners and domestic vacuum cleaners.
The outlet point of all of these devices involves discharge to the external pressure of a combination of fluids and particles.